The purpose of this work is to develop an efficacious vaccine for the prevention of Chlamydia trachomatis caused sexually transmitted diseases (STD) of humans. The project involves the study of immunity in a murine model of chlamydial infection of the female genital tract. The goal of the work is to identify mechanisms of protective immunity and protective antigens, information that then can used to formulate novel vaccines to test in this pre-clinical model. The long-range goal is to move the most promising of these vaccines to human clinical trials to assess their safety and efficacy in preventing chlamydial STDs. Past studies from this laboratory using gene knock out mice, adoptive transfer of immune T cells, and in vivo depletion of T cell subsets strongly implicate CD4+ Th1 cell mediated immunity as the major protective arm of the immune response against chlamydial genital infection. Conversely, CD8+ T cells, gamma/delta T cells, and antibodies play only a limited role in mediating protective immunity. We have continued studies along these lines to further define effector function(s) of CD4+ Th1 mediated immunity and lymphocyte homing to the genital mucosal. Our findings do not support a role for IFN-gamma, TNF-alpha, iNOS, or Fas mediated apoptopic killing in protective anti-chlamydial mediated T cell immunity. Homing studies implicate both systemic and mucosal integrins and their cognate receptors in lymphocyte homing to the genital mucosa. All attempts to generate protective CD4+ Th1 anti-chlamydial immunity at the genital mucosa using conventional DNA and recombinant antigen vaccine approaches have failed. Infection of the genital tract, or other mucosal sites, is the only highly efficacious way of generating protective immunity against chlamydial genital re-challenge. Because of the difficulty in vaccinating against chlamydial genital infection we have undertaken a novel albeit unconventional approach to chlamydial vaccine development. This approach utilizes adoptive transfer of autologous dendritic cells (DC) pulsed ex vivo with intact non-viable chlamydial organisms. Our results show that in vitro grown DC efficiently phagocytose inactivated chlamydiae. Chlamydial-pulsed DC, but not DC pulsed with inert latex beads, up-regulate the expression of class II, and the T cell co-stimulatory molecules CD40 and CD86. Chlamydial-pulsed DC also up-regulate the expression of T cell differentiating cytokines IL-6, IL-10, IL-12, and TNF-alpha and the chemokines; MIP-3, MIP-1, IP-10, and MCP-1. Chlamydial-pulsed DC were found to be highly efficient in presenting chlamydial antigen(s) to infection sensitized protective CD4+ Th1 cells. Mice adoptively immunized with chlamydial-pulsed DC produced a strong chlamydial specific Th-1 biased immune response. Moreover, immunized mice were found to be as immune to chlamydial genital challenge as post-infection immune animals. Thus, ex vivo antigen pulsed DC represent a very powerful approach for the study of protective immunity to chlamydial infection of the genital mucosa. The use of ex vivo antigen pulsed DC will provide a way to identify chlamydial protective antigens and key immune effector functions that elicit protective immunity at the genital mucosa. Future studies will focus on using DC pulsed ev vivo with DNA based or recombinant protein antigens. These studies should yield information important to the development of more conventional vaccines for the prevention of chlamydial STDs.